(a) Field of the Invention
The present invention relates to a transmission symbol detection method in a multiple antenna system. Particularly, it relates to a transmission symbol detection method in a multiple antenna system including a plurality of transmitting antennas.
(b) Description of the Related Art
For a mobile communication system such as IEEE 802.16e that uses four transmitting antennas, three usable space-time codes are defined for transmission. The three space-time codes are denoted as three matrixes A, B, and C, and each has a different symbol transmission rate and a different diversity gain. Particularly, the space-time code B has good tradeoff performance in symbol transmission rate and diversity gain, and can be represented as shown in Equation 1.
                    B        =                  [                                                                      s                  1                                                                              -                                      s                    2                    *                                                                                                s                  5                                                                              -                                      s                    7                    *                                                                                                                        s                  2                                                                              s                  1                  *                                                                              s                  6                                                                              -                                      s                    8                    *                                                                                                                        s                  3                                                                              -                                      s                    4                    *                                                                                                s                  7                                                                              s                  5                  *                                                                                                      s                  4                                                                              s                  3                  *                                                                              s                  8                                                                              s                  6                  *                                                              ]                                    [                  Equation          ⁢                                          ⁢          1                ]            
Here, the vertical axis denotes an antenna, and four symbols are simultaneously transmitted from four antennas. The horizontal axis denotes time or carrier frequency.
When symbols are transmitted by using the above-given space-time codes, the symbols are simultaneously received at a receiving side, and therefore the entire performance of the system greatly depends on a detection method of the receiving side. Among many conventional detection methods, the maximum likelihood (ML) detection method results in the best performance.
However, the ML detection method is very complex. Particularly, the ML detection method has a drawback of being incapable of real-time detection since the system complexity increases as the size of the constellation (e.g., 16-QAM or 64-QAM) increases.
Accordingly, in order to reduce system complexity while providing the best performance (i.e., ML performance), a sphere decoding method has been proposed. The sphere decoding method detects constellation points that are close to a received signal, and therefore the system complexity is lower than a simple ML detection method. However, the sphere decoding method has a problem of complexity, and, in the worst case, the sphere decoding method causes exponential functional complexity so that there still exists a problem in application of the sphere decoding method to an actual system.
Therefore, in order to fundamentally decrease the system complexity, methods that can provide suboptimal performance need to be considered, and the methods include zero-forcing (ZF), minimum mean squared error (MMSE), ZF with successive interference cancellation (ZF-SIC), and MMSE with SIC. However, those methods provide suboptimal performance that is more deteriorated than the performance of the ML detection method.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.